National Marine Ecosystem Diagnostic Analysis (MEDA) ASCLME. Agulhas and Somali Current Large Marine Ecosystems (ASCLME) Project

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1 Ta n z a n i a National Marine Ecosystem Diagnostic Analysis (MEDA) Agulhas and Somali Current Large Marine Ecosystems (ASCLME) Project ASCLME Agulhas and Somali Current Large Marine Ecosystems Project

2 The GEF unites 182 countries in partnership with international institutions, non-governmental organizations (NGOs), and the private sector to address global environmental issues while supporting national sustainable development initiatives. Today the GEF is the largest public funder of projects to improve the global environment. An independently operating financial organization, the GEF provides grants for projects related to biodiversity, climate change, international waters, land degradation, the ozone layer, and persistent organic pollutants. Since 1991, GEF has achieved a strong track record with developing countries and countries with economies in transition, providing $9.2 billion in grants and leveraging $40 billion in co-financing for over 2,700 projects in over 168 countries. www. thegef.org UNDP partners with people at all levels of society to help build nations that can withstand crisis, and drive and sustain the kind of growth that improves the quality of life for everyone. On the ground in 177 countries and territories, we offer global perspective and local insight to help empower lives and build resilient nations. This document may be cited as: ASCLME National Marine Ecosystem Diagnostic Analysis. Tanzania. Contribution to the Agulhas and Somali Current Large Marine Ecosystems Project (supported by UNDP with GEF grant financing). The contributions of the Western Indian Ocean Marine Science Association (WIOMSA) in supporting this publication are gratefully acknowledged The contributions of the Ocean Data Information Network of Africa (ODINAFRICA) in supporting this publication are gratefully acknowledged. The views expressed in this publication may not necessarily reflect those of the GEF, UNDP, or other UN agencies or project partner institutions/organisations. Neither does it imply any opinion whatsoever as to the legal status of any country, territory, city or area, of its authorities, or of the delineation of its territories or boundaries.

3 e L a k T RWANDA 2 Ngara BURUNDI 4 6 a Kasulu Kigoma n Ujiji g a n y DEMOCRATIC REPUBLIC OF THE CONGO 8 i k a Mpanda ZAMBIA UGANDA L. Rushwa Buoen Kibondo Moyowosi Sumbawanga Mpui Bukoba Geita MWANZA SHINYANGA L. Eyasi Kahama Shinyanga Gombe Igombe Tobora Kaliua Tunduma Lake Victoria Musoma KIGOMA Biharamulo Game Res. K A G E R A Ugalla W ala R U K W A KATAVI N.P. Ugalla River Game Res. Rubondo I. Rungwa UNITED REPUBLIC OF TANZANIA National capital Provincial capital Town, village Airport International boundary Provincial boundary Main road Secondary road Railroad Ukara I. Ukerewe I. Maisome I. Shama Lake Rukwa Mbeya Mwanza Piti Nzega Limba Tukuyu Mhawara TABORA Chunya Sim iyu M B E Y A M A W I A Steppe Iwembere Rungwa Game Reserve L Mara Singida Great L a MARA k e SERENGETI NAT. PARK Maswa Game Res. L. Kitangiri S I N G Njombe N y a s a I D Ruaha A Njombe Babati Manyoni Kisigo RUAHA NAT. PARK KIPENGERE RANGE Songea Lake Natron Ngorongoro Conservation Area Lake Manyara IRINGA Kilombero Masai Steppe Kondoa Iringa Arusha Dodoma DODOMA Great Luwegu R U V U M A The boundaries and names shown and the designations used on this map do not imply official endorsement or acceptance by the United Nations. MT. KILIMANJARO NAT. PARK TARANGIRE NAT. PARK Moshi Mpwapwa Ruaha Same Morogoro Mbarangandu Pangani ARUSHA M O M O Z KENYA Kilimanjaro 5895 m MIKUMI N.P. R O Tunduru Mkomazi Handeni O G O R Rufiji KILIMANJARO Wami Korogwe T A N Selous Game Reserve A M B I Sadani Kibaha Matandu Nachingwea Mkomazi Game Res. Tanga PWANI Rufiji Utete Mohoro LINDI Mbemkuru INDIAN Wete Pemba Pangani ZANZIBAR Zanzibar 6 Zanzibar Lindi Dar es Salaam OCEAN Mafia I. Kilwa Kivinje Mtwara Masasi MTWARA Newala Ruvuma UNITED REP. OF TANZANIA G A Q U E DAR ES SALAAM 300 km mi Map No Rev. 6 January 2006 UNITED NATIONS Department of Peacekeeping Operations Cartographic Section

4 Table of Contents Table of Contents Executive Summary....iv Acknowledgements v Contributing Experts and their Institutions...vi List of Acronyms.... vii 1. Country Overview Biophysical Environment Description of the coast and distinctive features Climate Marine and coastal geology and geomorphology Fresh water resources and drainage Physical Oceanography Currents Tidal regime and waves Tidal ranges Wave patterns Sea level change Ocean temperature Sea Surface Temperature (SST) Salinity patterns Water masses of the Tanzanian coast Ocean-atmosphere interaction Chemical and Biological Oceanography Nutrients Persistent organic pollutants Primary production Secondary production Coastal Zone and Continental Shelf Description and extent of coastal and marine habitats Coral reefs Mangroves Seagrass beds Productivity of the Coastal zone Coral reefs Mangroves Seagrass beds Microfauna and meiofauna Meiofauna status in Marine Ecosystems of Tanzania Microfauna status in the Marine Ecosystems of Tanzania Macrofauna Invertebrates Prawns/shrimps Artisanal Fisheries Landings Stock Assessments Lobsters Cephalopods Squid and Cuttlefish Sea cucumbers Shells Fish and fish resources Mammals i

5 Table of Contents Reptiles Birds Exotic and Invasive Species Long term predicted atmospheric changes Air temperature and rainfall Wind patterns Extreme events Human Environment Coastal and island populations Cultural diversity Age and gender structure Sites of religious or cultural significance Health situation and health service delivery Infrastructure Harbours Airports Energy Coastal Livelihoods Small-Scale Fisheries Tourism Mariculture Agriculture and Forestry Energy Ports and Coastal Transport Coastal Mining Conclusions Policy and Governance Planning and Management National Disaster Management Plans Environmental Sensitivity Mapping Coastal Management/Development Plans Areas under special management Marine Protected Areas Marine Managed Areas Monitoring, Control and Surveillance Cost-Benefit Analysis Coastal Agriculture Coastal Forestry Value of critical ecosystems Tourism Ports and Harbours Coastal Mining Coastal Resources and Poverty Alleviation References ii

6 Table of Contents ANNEXES I Extended bibliography II. Metadata records III. Capacity building and training review and work programme IV. Areas of Concern (extracted from each of the MEDA chapters) V. Policy and Governance Report VI. Requirements for data collection, analysis (processing/modeling/integration) or repatriation to inform the national MEDA. VII. National projects recently undertaken or currently underway which are relevant to the ASCLME MEDA, TDA or SAP. VIII. Official designation of territorial waters; other statutes relating to marine governance. IX. National Data and Information Management Plan X. DLIST summary report XI. National Local Economic Development Plan (DLIST) XII. Coastal Livelihoods Assessment Report XIII Inshore Oceanographic Monitoring Plan XIV. National Causal Chain Analysis Report iii

7 Executive Summary Executive Summary Tanzania is located on the East coast of Africa, bordering the Indian Ocean, and lies between Kenya to the north and Mozambique to the south. Its total area is 945,087 km 2 and this includes the islands of Mafia, Pemba and Zanzibar. Water covers 59,050 km 2 of this area and the coastline along the Indian Ocean is 1,424 km. The population of the country is 40 million with a growth rate of 2.6%. The economy is largely dependent on agriculture, which accounts for about 48% of the GDP. Tanzania is endowed with a scenic, diverse and resource rich coastal area. This strip of land and water supports a diversity of important natural systems, including coral reefs, beaches, estuaries, sea grass beds and extensive mangrove stands. Tanzania s coastal and marine ecosystems cover the mainland coast, three major islands (Pemba, Unguja, and Mafia) all of which are less than 100 km offshore, numerous small near-shore islands and islets and one oceanic island, Latham Island. The continental shelf covers an estimated 17,500 17,900 km 2. Demersal fish species dominates marine catches with a total catch of 22,290 tons compared to a pelagic catch of 14,014 tons. The main commercial marine species are sardine and anchovy, which together form percent of total fish landings. The artisanal marine fishery sub-sector employs more than 29,754 full time fishers, using about 7,190 relatively small fishing canoes (Fisheries Division, 1992). The majority of the coastal communities rely on coastal resources for their livelihood. The coast is of immense strategic importance to many social and economic sectors such as shipping, fishing, tourism, trade, agriculture, settlements and industrial developments. Recently, Tanzania has experienced a significant increase in coastal tourism, mariculture development and natural gas exploitation. Livelihood opportunities for people living along the Tanzanian coastline are changing; coastal areas are experiencing rapidly expanding population, putting increasing pressure on limited resources. As farming employment optiosn decline as a result of lack of financial assistance in the agricultural sector, more people are forced to depend on the easy and very common pool of coastal resources, such as forests, fisheries,coastal land areas, swamps, mangroves and coral reefs. The productivity of these resources is in decline as the environmental carrying capacity decreases due to increased coastal pollution, depletion of fish stocks and coastal resources, extinction of species overall decline in water quality. The coast s untapped potential must be harnessed, but it must be done with the appropriate safeguards that link growth to wise management. The pressures on these resources will grow and, like other countries faced with an expanding population, are at risk of collapse. People s quality of life, which is inextricably tied to the resource base, will continue to decline unless development moves hand in hand with local goals and aspirations. iv

8 Acknowledgements Acknowledgements We would like to express our sincere gratitude to the Government of the United Republic of Tanzania and the Revolutionary Government of Zanzibar for supporting this initiative and efforts both in kind and materially throughout from the start to the end. The Government of the United Republic of Tanzania through its Ministry of Livestock Development and Fisheries; the University of Dar es Salaam through its Colleges of Natural and Applied Sciences (CoNAS) and Arts and Social Sciences (CASS), and the Institute of Marine Sciences (IMS); the Tanzania Fisheries Research Institute (TAFIRI); and the National Environment Management Council (NEMC) are thanked for providing and supporting the experts who prepared this document. The NEMC, the Focal Institution for the ASCLME project in Tanzania, is highly thanked for providing administrative guidance and support of the MEDA process in close collaboration with the IMS which was coordinating the process. The local stakeholders played a key role in guiding the coverage of contents of the document through the several national workshops that were organized. Several regional and international experts provided assistance in the preparation of the Tanzania Marine Ecosystem Diagnostic Analysis (MEDA). Finally, we would also like to thank all who assisted the experts who prepared this document in one way or another including providing them with the relevant data and or information. These include scientists, researchers, stakeholders, local communities, Non-Governmental Institutions (NGOs), Institutions and many others. The MEDA is a national contribution to the multinational Transboundary Diagnostic Analyses (TDA) - Strategic Action Programme (SAP) process, and was funded and supported by the Agulhas and Somali Current Large Marine Ecosystems Project (which is funded by the Global Environment Facility and implemented by the United Nations Development Programme). The ASCLME Project Coordination Unit is thanked for ongoing support of the MEDA process. The Western Indian Ocean Marine Science Association (WIOMSA) and the Forum for Heads of Marine Related Institutions (FARI) are thanked for coordinating the peer review process, v

9 Contributing Experts and their Institutions Contributing Experts and their Institutions s/n Expert Name Institution 1 Dr Razack B LOKINA University of Dar es Salaam College of Arts and Social Sciences (CASS) Department of Economics P.O. Box Dar es Salaam 2 Dr Yohanna W SHAGHUDE University of Dar es Salaam Institute of Marine Sciences (IMS) P.O. Box 668 Zanzibar 3 Mr Shigalla MAHONGO Tanzania Fisheries Research Institute (TAFIRI) P.O. Box 9750 Dar es Salaam 4 Dr Sadri A SAID University of Dar es Salaam Institute of Marine Sciences (IMS) P.O. Box 668 Zanzibar 5 Dr Vedast M MAKOTA National Environment Management Council (NEMC) Regent Estate Plot No. 29/30 P.O. Box Dar es Salaam 6 Dr Daniel A SHILLA University of Dar es Salaam College of Natural and Applied Sciences (CoNAS) Department of Aquatic Sciences and Fisheries P.O. Box Dar es Salaam 7 Mr Winfried V HAULE Ministry of Livestock Development and Fisheries Fisheries Division PO Box 9152 Dar es Salaam The work was coordinated by: Prof. Dr. Desiderius C.P MASALU National Data and Information Coordinator (ASCLME) University of Dar es Salaam Institute of Marine Sciences (IMS) P.O. Box 668 Zanzibar vi

10 List of Acronyms List of Acronyms ACEP: ASCLME: CBO: CORDIO: DLIST: DoF: EEZ: EIA: ENSO: FAO: GDP: GIS: GMDSS: GPA: GOOS: GTS: HABs: HEP: IBAs: ICZM: ISSG: IOC-UNESCO: IOD: IOTWS: ITCZ: IUCN: JMA: MACEMP: TAFIRI: TCMP: TIO: TPA: TMA: MPAs: MCS: NEMC: NGO: NPA: NORAD: PSU: PTWC: POPs: SADC: SST: SWIOFP: SWOT: UNDP: UNEP: UNESCO: URT: USAID: USD: VTMS: African Coelacanth Ecosystem Programe Agulhas and Somali Current Large Marine Ecosystems Community Based Organisation Coastal Oceans Research and Development in the Indian Ocean Distance Learning Information Sharing Tool Department of Fisheries Exclusive Economic Zone Environmental Impact Assessment El Nino / La Nina Southern Oscillation Food and Agriculture Organization Gross Domestic Product Geographic Information System Global Maritime Distress Signalling System Global Programme of Action for Protection of Marine Environment Global Ocean Observing System Global Telecommunications System Harmful Algal Blooms Hydro-Electric Power Important Bird Areas Integrated Coastal Zone Management Invasive Species Specialist Group Inter-Governmental Oceanographic Commission of UNESCO Indian Ocean Dipole Indian Ocean Tsunami Warning System Inter-Tropical Convergence Zone The World Conservation Union Japan Meteorological Agency Marine and Coastal Area Environmental Management Project Tanzania Fisheries Research Institute Tanzania Coastal Management Partnership Tanzania Indian Ocean Tanzania Ports Authority Tanzania Meteorological Agency Marine Protected Areas Monitoring, Control and Surveillance National Environmental Management Council Non-Governmental Organisation National Programme of Action Norwegian Agency for International Development Practical Salinity Units Pacific Tsunami Warning Center Persistent Organic Pollutants Southern Africa Development Community Sea Surface Temperature World Bank-GEF South-West Indian Ocean Fisheries Project Analysis of Strengths, Weaknesses, Opportunities and Threats United Nations Development Programme United Nations Environment Programme United Nations Educational, Scientific and Cultural Organisation United Republic of Tanzania United States Agency for International Development United States Dollar Vessel Tracking Management System vii

11 List of Acronyms WCS: WHO: WIO-LaB: WIO: WWF-EAME: World Conservation Society World Health Organization UNEP-GEF Project Addressing Land-Based Sources and Activities in the WIO Western Indian Ocean World Wildlife Fund Eastern Africa Marine Ecoregion viii

12 1. Country Overview 1. Country Overview The United Republic of Tanzania is the largest country in East Africa covering a surface area of about 945,200 km 2. It consists of two parts; the mainland with an area of 942,800 km 2 and Zanzibar Islands (Unguja Island and Pemba Island) which occupy an area of 2,400 km 2. Approximately 60,000 km 2 of the total area of Tanzania consists of inland water bodies. Tanzania lies just south of the equator, between latitudes 1 o -11 o 45 S and longitudes 29 o o 25 E. The country shares its borders with eight countries, namely Kenya and Uganda to the north; Rwanda, Burundi, Democratic Republic of Congo and Zambia to the west and Malawi and Mozambique to the south. Tanzania has an abundance of inland water bodies with several lakes and rivers. Lake Tanganyika runs along the western border and is Africa s deepest and longest freshwater lake and world s second deepest lake. Lake Victoria to the north is the world s second largest lake draining into the Nile River and then to the Mediterranean Sea. The Rufiji River is Tanzania s largest river that drains into the Indian Ocean south of Dar es Salaam. Although there are many rivers, only the Rufiji and Kagera are navigable. Tanzania s coastal and marine ecosystems cover the mainland coast, three principal islands (Pemba, Unguja, and Mafia) all of which are less than 100 km offshore, numerous small near-shore islands and islets and one oceanic island, Latham Island. The continental shelf, covering an area estimated to range between17,500 and 17,900 km 2 (up to a depth of 200 m) is generally narrow with the narrowest point being 2 km and the widest 80 km. The shelf drops sharply after a depth of 60 m. Pemba and Latham islands are separated from the mainland by relatively deep water channel (about m and m deep, respectively). Pemba Island is believed to have been part of the mainland that broke away about 10 million years ago. Unguja and Mafia are coral limestone islands established on the continental shelf and were probably part of a Pleistocene inshore coral reef system which is now separated from the mainland by relatively shallow (30-50 m deep) channels (McClanahan 1988). Tanzania s Great Rift Valley is the country s most distinctive geological feature which was caused by faulting throughout eastern Africa. The Rift Valley is associated with volcanic activity in the north-eastern regions of the country (UN 2002). This faulting led into the formation of two branches of the Great Rift Valley; the western branch which holds Lakes Tanganyika, Rukwa, and Nyasa and the eastern branch that ends in northern Tanzania and includes Lakes Natron, Manyara, and Eyasi ( country_profiles/ stm?). Except for a narrow belt of 900 km 2 along the coast, most of Tanzania lies at an elevation above 200 m above sea level. Much of the country is higher than 1,000 m above sea level (United Republic of Tanzania 2005a). Mount Kilimanjaro located in the north east of the country rises to 5,895 m above sea level - the highest point in Africa. Tanzania s climatic conditions are characterized by a long dry spell from May to October, followed by a rainy season between November and April. The main rainy season along the coast and Mount Kilimanjaro region is from March to May, with short rains occurring in the period between October and December. In the western part of the country, in the Lake Victoria basin, rainfall is high and well distributed throughout the year, with the peak rainy season occurring in the period between March and May (Mongi, et al., 2010). Agriculture, which comprises crop, animal husbandry, forestry, fishery, and hunting subsectors, plays a key role in the Tanzanian economy. It contributes the largest share to the gross domestic product (GDP). Major exports include coffee, cotton, tea, tobacco, cashew nuts, and sisal. The economy has been growing between 6.7% and 7.8% over the past seven years (United Republic of Tanzania 2009). Despite this impressive economic growth, there has been relatively limited improvement in infrastructure, education and health sectors. Poverty remains high in both urban and rural areas. The growth has remained inadequate to meet development and poverty reduction objectives of the National Strategy for Growth and Reduction of Poverty. The current growth is mainly attributed to the growth in a number of subsectors, mainly agriculture, commerce, tourism (including hotels and restaurants), transport and communication, and financial and business services (United Republic of Tanzania 2005a). The government has put in place measures to sustain the current economic growth rate and reduce nationwide poverty, through the promotion of the private sector participation in the economy. The current population is estimated to be 40 million with the mainland Tanzania registering a relatively lower population growth rate of 2.9% as compared to Zanzibar (Table 1). There are however large variations in 1

13 1. Country Overview population growth rate from one region to another (United Republic of Tanzania 2006a). About 51% of the regions in Tanzania have their population growing at a rate above 2.5% per annum and about 71% of the regions have their population growing at a rate above 2% per annum (Figure 1). Table 1: Population growth in the thirty five years from (United Republic of Tanzania 2005b) Total Population Growth rate Tanzania Mainland Tanzania Zanzibar 11,958,654 17,036,499 22,455,205 33,461, , , , , While the population of Tanzania has nearly trebled in the last four decades, the country is still sparsely populated. Population density is however high in some parts of the country. The current population density is estimated to be above 39 persons per square kilometre. The high population growth rate is attributed to high fertility rate and declining mortality levels. According to the 2002 Population and Housing Census, the life expectancy at birth is 51 years (United Republic of Tanzania 2005b). The population is predominantly rural but the proportion of urban residents has been increasing over the years (Table 2). Table 2: Basic Demographic Indicators (Sources: URT 1967, 1978, 1988, 2002) Selected Demographic Indicators for Tanzania Indicators Year Population (millions) Intercensal growth rate (percent) Sex ratio Crude birth rate Total fertility rate Crude death rate Infant mortality rate Percent urban Density (pop/km2) Life expectancy at birth (years)

14 1. Country Overview Figure 1: The grouping of population growth rates in regions of Tanzania (URT 2006a) 3

15 2. Biophysical Environment 2. Biophysical Environment 2.1 Description of the coast and distinctive features The coast of Tanzania includes a narrow coastal belt varying in width from 20 to 150 km on the Tanzania Mainland, the offshore waters and the associated islands (Kent et al., 1971). The narrow coastal belt along the Tanzania Mainland runs more or less in a northerly direction for 800 km (Figure 2). This narrow belt is characterized by low-lying coastal plains which rise towards the hinterland to an elevation of about 200 m at the border with the inland plateau (Macmillan 2008). Low-lying coastal plains are also a characteristic feature for the offshore islands, but the highest altitudes on the islands are generally lower than those on the Mainland (Macmillan, 2008; Kent et al. 1971). The coastal plains on the islands generally lie between 0 and 100 m above mean sea level. The coastal belt along the Tanzania Mainland is widest along the Dar es Salaam embayment where it extends 150 km inland (Kent et al. 1971, Kapilima 1984). However, it is relatively narrow north and south of the Dar es Salaam embayment where its width is about 20 km (Kent et al. 1971). The three major Islands, Pemba, Unguja and Mafia, are all located within 100 km of the Tanzania Mainland coastline. While Pemba is separated from the Tanzania Mainland by a deep channel (800 m), Unguja and Mafia are separated by a relatively shallow channel whose depth is less than 65 m (Mpanda, 1997; Shaghude and Wannäs, 1998; Shaghude, 2001 & 2003). Both Unguja and Mafia lslands are situated on the continental shelf, while Pemba is located off the continental shelf (Figure 3). DRC UGANDA RWANDA L. Victoria KENYA BURUNDI L. Eyasi L. Natron L. Manyara Pemba Is. L. Tanganyika TANZANIA Dar es Salaam Unguja Is. L. Rukwa Mafia Is. ZAMBIA Coastal Tanzania Ocean/Lakes National Boundaries 0 Km 200 MALAWI L. Nyasa MOZAMBIQUE Figure 2: The extent of the coastal belt of Tanzania (Redrawn after Macmillan 2008) 4

16 2. Biophysical Environment Figure 3: The coastal region of Tanzania including the three major Islands (Source: Shaghude, 2001) The most prominent primary coastal types along the coast of Tanzania (Figure 4) include: 1- The fringing reef coast with or without beach plains; 2- Patchy reef coast, either with fossil reef terraces and islands or with sand spits, and; 3- Exposed low-lying coasts. 5

17 2. Biophysical Environment Hinterland FRINGING REEF COAST Reef Limestone Terrace Rock Cliff Backreef Platform Fringing Reef OCEAN HW (a) Without Beach Plain Intertidal FRINGING REEF COAST Hinterland Rock Cliff Fringing Reef Beach Reef Terrace Beach Plain Backreef Platform OCEAN HW (b) With Beach Plain Lagoon Intertidal (c) OCEAN PATCH REEF COAST OCEAN (d) PATCH REEF COAST Figure 4: Shore sections showing the most prominent coastal types in Tanzania, namely the fringing reef coasts (a-b), patch reef coasts (c-d) Exposed low lying sand costs (e) (Modified from Kairu and Nyandwi, 2000) Most of the three primary coastal types also host sheltered tidal inlets, estuaries and creeks. Prime examples of fringing reef coast include much of the eastern coasts of the Unguja and Pemba islands (Arthurton, 2003), while examples of patch reef coasts include much of the western coasts of Pemba, Unguja and Mafia, a number of coastal stretches along the Tanzania Mainland proximal to Tanga, Pangani (Shaghude, 2006), Bagamoyo, Dar es Salaam (Shaghude et al,. 2006) and Mnazi Bay. An example of the exposed low-lying sand coast is the coastal section between Mkwaja and Sadani (Shaghude, 2006). Tidal inlets, estuaries and creeks are all associated with well developed mangrove forests and in some instances they are also sites of urban and port development, for example Tanga and Dar es Salaam (Kairu and Nyandwi, 2000). 6

18 2. Biophysical Environment Apart from the three major islands mentioned above, there are numerous chains of small islands along the coast (Francis et al., 2001). Most of these islets occur as raised fossil Pleistocene reef platforms or sand banks. The typical examples include Tumbatu, Changuu, Bawe, Chapwani, Chumbe, Latham and Mnemba (off Unguja Island), Bongoyo, Mbudya, Pangavini, Fungu Yasin, and Makatumbe of the Dar es Salaam Marine Reserve (Wagner, 2007). Some of the islets such as Tumbatu are large enough to support human settlements but others are either too small or lack freshwater resources necessary for supporting human settlements (Francis et al,. 2001). However, most of these islets are of significant ecological and socio-economic importance, supporting terrestrial vegetation and fauna as well as providing recreational services for tourists and temporary homes for fishermen. 2.2 Climate The climate of the coastal region of Tanzania is characterized by tropical humid conditions. Two major factors influence the climate namely; the geographic location within latitudes 4 o o 30 S, which creates a truly tropical/equatorial setting, with high temperatures, high humidity and low wind speeds, and secondly its position along the eastern edge of Africa, which places it under the influence of the seasonal monsoon wind regime (Francis et al., 2001). The monsoon wind changes affect not only the coast of Tanzania but also the entire Western Indian Ocean (WIO) region (Ngusaru, 1997). They are characterized by two seasonal cycles; the South East (SE) monsoon season from April to October and the North East (NE) monsoon season from November to March (Shaghude and Wannäs, 1998). The SE and NE seasonal monsoon winds in Tanzania are locally known as the Kusi and Kaskazi, respectively. The monsoon wind patterns have marked effect on the patterns of air and water temperatures, winds and rainfall (Ngusaru, 1997) The SE monsoon is generally characterized by relatively lower air temperatures (about 25 o C), relatively stronger wind speeds and long rainy season. In contrast, the NE monsoon is characterized by relatively higher air temperatures (>30 o C), relatively weaker wind conditions and short rainy season. The months of March-April and October-November are the inter-monsoon periods, locally known as the Matlai and the wind conditions during these periods are calmest. Strongest winds along the coast are experienced during June- July period. Occasionally, the SE monsoon is also associated with storms and cyclones (Francis et al., 2001). Despite this wide generalization of the climate along the coast of Tanzania, there are local variations which are generally influenced by the north-south geographic variation as well as the effects of sea breezes on the coast. Much of the northern parts of the coast of Tanzania (including Dar es Salaam, Tanga, Pemba and Unguja) are characterized by a bimodal rainfall regime, with two rainfall peaks in a given year; a long rainy season from March to May with a peak in April and a short rainy season from October to December with a peak in November (Nyenzi et al.,1999, Francis et al., 2001). In contrast, much of southern Tanzania (including, Mtwara, Lindi and Mafia) is characterized by a unimodal rainfall regime, with a continuous rainfall season between December and April (Francis et al,. 2001). Rainfall along the coast of Tanzania generally increases northwards (Figure 5) but the islands receive relatively higher rainfall compared to corresponding coastal areas along the Tanzania mainland. Pemba receives the highest annual rainfall (1916 mm) followed by Mafia (1877 mm) and Unguja (1565 mm), while Lindi receives the lowest amount of rainfall (917 mm) (Francis et al. 2001). As for the wind speeds, Mtwara experiences the highest wind speeds of up to 35 knots, compared to other areas along the coast of Tanzania such as Tanga, Dar es Salaam and Zanzibar, where the mode wind speed is 20 knots (Dubi, 2001). There is also local variation in the timing of the occurrence of the peak wind speeds. According to Dubi (2001), Tanga, Dar es Salaam and Mtwara experience peak wind speeds in the period between July and August while Zanzibar experiences peak wind speeds in January. 7

19 2. Biophysical Environment 600 Tanga mm 0 J F M A M J J A S O N D 600 Pemba mm 0 J F M A M J J A S O N D 600 Zanzibar Town mm 0 J F M A M J J A S O N D 600 mm Dar es Salaam 0 J F M A M J J A S O N D 600 Mafia mm 0 J F M A M J J A S O N D 600 mm Lindi 0 J F M A M J J A S O N D 600 Mtwara mm 0 J F M A M J J A S O N D Figure 5: Annual average rainfall distribution along the Coast of Tanzania (Source: Francis et al. 2001) I) Issues Environmental variability and unpredictability particularly flooding and storm events ii) Gaps Analyses of pattern/frequency of extreme climatic events along the coast of Tanzania 2.3 Marine and coastal geology and geomorphology The coastline of Tanzania with its major islands is about 1,424km long. Along the Tanzania mainland the distinction between the coastal belt and inland plateau is based on rock formations (Alexander 1969, Kent et al., 1971). The bedrock geology of the coastal belt is characterized by sedimentary rocks which vary in age from Jurassic, Cretaceous to Tertiary and Quartenary (Kent et al., 1971). The sediments forming the sedimentary rocks are from both marine and terrestrial sources (Kent et al., 1971, Kapilima, 1984). In contrast, the interior plateau is dominated by metamorphic crystalline rocks (Alexander 1969, Kent et al,. 1971) of the Mozambique belt, believed to have been formed about 550 ± 100 millions years ago (Windley, 1986). The three islands, Pemba, Unguja and Mafia are part of the ancient Miocene Pangani/Ruvu/Rufiji river deltas (Kent et al., 1971; Mruma, 1996). Due to eustatic movements and block faulting over the coast and offshore deltaic zone, at present these islands remain above the sea level as land blocks off the original deltas (Mruma, 1996). The bedrock geology of the three Islands of Pemba, Unguja and Mafia is characterized by relatively younger sedimentary rocks, ranging in age from Miocene to Quaternary (Kent et al,. 1971). The structural trend and the evolution of the coastal basin are closely connected to the Karroo and the Cenozoic 8

20 2. Biophysical Environment rifting as well as the opening of the Indian Ocean (Kent et al., 1971; Shaghude et al., 1994; Shaghude and Wannas, 1998). A series of transgressions and regressions related to these events resulted in the deposition of thick sediment sequences in the coastal basin (Shaghude et al., 1994; Shaghude and Wannas, 1998). There are two major structural trends which dominate the coastal basin (Figure 6), namely the Tanga Fault with a NNE-SSW direction, which swings to NW in other places, such as Dar es Salaam, Bagamoyo and Zanzibar and the Lindi fault with a NNW SSE direction (Kent et al., 1971; Mruma, 1996; Mpanda, 1997). Both the Tanga and Lindi tectonic directions were initiated at least during the Karroo time and have influenced both the geomorphology of the coast and the coastal basin in general (Kent et al,. 1971). The geomorphology of Pemba is for instance controlled by the Tanga fault trend, whereas that of Unguja Island is a result of superposition of both the Tanga and Lindi fault trends (Mruma, 1996). Beach ridges and marine terraces are among the most prominent backshore features along the coast of Tanzania. These distinctive geomophological features, which help to unlock the late Holocene to Pleistocene sea level fluctuations (Muzuka et al., 2004), have been discussed by many previous studies (Alexander 1968, 1969, 1985; Muzuka et al., 2004). Alexander (1968) distinguished three marine terrace units along the northern parts of the Tanzania mainland coast (from Dar es Salaam to Tanga) which were named as the Sakura (the highest and oldest terrace unit), the Tanga (the next lower terrace unit) and the Mtoni (the lowest and youngest terrace unit). Each terrace unit represents a major phase of sea level fluctuations (Alexander 1969; Muzuka et al,. 2004). The marine terraces on Pemba and Unguja islands are similar to those discussed by Alexander (1969) on the Tanzania mainland in that all of them consist of steps of coral limestones indicative of marine and tectonic origin (Muzuka et al,. 2004). Like the marine terraces, beach ridges are common geomorphological features on the mainland as well as on the major islands, being most prominent on the Mtoni terrace unit. The information on sea bottom sediment composition, distribution and morphology is generally scarce apart from limited studies conducted in the Zanzibar channel and between Pangani and Wami rivers (Shaghude et al. 1998, Shaghude 2003, 2004a, 2004b). The problem of shoreline change, particularly coastal erosion has increasingly become one of the major issues of environmental, ecological and socioeconomic concern in Tanzania, including the islands of Zanzibar (Shaghude et al., 2004; UNEP-GPA, 2004). 9

21 2. Biophysical Environment 5 Fault systems Tanga Pemba Is. 6 7 Ngerengere Lugoba Ruvu TANGA FAULT ZONE Zanzibar Is. Dar es Salaam Pugu Hills 8 Kidodi Nyakatitu INDIAN OCEAN Mafia Is. INDIAN OCEAN LINDI FAULT ZONE 9 Kiswere 10 Lindi 0 Km 100 Mtwara Figure 6: Map of coastal Tanzania showing the major fault trends. The orange, blue and black fault systems represent the three phases of faulting, namely, Karroo and later faulting, Jurassic and later faulting and Miocene and later faulting, respectively (Source: Mruma, 1996) I) Issues The ecological and socio-economic impacts due to coastal erosion are increasingly becoming issues of major concern. Poor management of the shores due to lack of understanding of coastal erosion causative factors and sustainable mitigation/adaptation measures. ii) Gaps Most of the existing information on the marine and coastal geology and geomorphology are drawn from studies conducted on the northern parts of Tanzania (from Dar es Salaam to Tanga). There is limited information on the southern parts of the country (between Dar es Salaam and Mtwara). Information on the sea bottom morphology (bathymetry) is currently lacking for many coastal parts of Tanzania. This is important for running of hydrodynamic models. 10

22 2. Biophysical Environment 2.4 Fresh water resources and drainage The coastal region of Tanzania has several rivers that discharge into the Indian Ocean. The coastal drainage system covers about 20% of the country and contributes about 50% of the total surface runoff (Francis et al., 2001). The Rufiji is the largest river on the Tanzanian Indian Ocean (TIO) drainage system. Its mean annual discharge is estimated to range between 900 and 1,133 m 3 /s. The river contributes 50% of the total fresh water discharges to the sea (Welcomme, 1972; Hafslund 1980; Francis et al., 2001). Other important rivers include the Ruvuma with a mean annual discharge of 475 m 3 /s, the Wami with a mean annual discharge of 63 m 3 /s, the Ruvu with a mean annual discharge of 63 m 3 /s and the Pangani with a mean annual discharge of 27 m 3 /s (Welcomme, 1972; Francis et al., 2001; IUCN, 2003; Mikiyasu, 2007). The remaining rivers such as the Matandu, Mbwemkuru and Lukuledi are considered to be relatively less important in terms of freshwater discharges to the Indian Ocean (Figure 7 and Table 3). Figure 7: River systems draining into the coast of Tanzania (Modified after Francis et al. 2001) 11

23 2. Biophysical Environment Table 3: Major and Minor rivers along the Tanzanian Indian Ocean Drainage system (Modified from Welcomme, 1972; Francis et al., 2001) River Length (km) Catchment area ( 000 km 2 ) Mean annual discharges (m 3 /s) Rufiji Ruvuma (in Tanzania) 475 Wami Ruvu Pangani Matandu Mbwemkuru Likuledi The flow pattern of all the rivers is directly related to the general rainfall pattern (Welcomme, 1972; Hafslund, 1980; Francis et al., 2001; Duvail and Hammerlynck, 2007). Relatively higher river discharges occur during the period November- May (peak flow in March-April) and lower discharges occur during the dry season from June to October (Figure 8) The hydrograph of the Rufiji (flow in cumecs) Jan-58 Jan-60 Jan-62 Jan Kilombero Luwegu Jan-66 Jan-68 Jan-70 Jan-72 Jan-74 Jan Jan-76 Jan-78 Jan-80 Jan-82 Jan-84 Figure 8: The hydrograph of the Rufiji River (Modified from Hafslund 1980). 12

24 2. Biophysical Environment The mouths of most of these rivers are characterized by the presence of deltas, estuaries and mangrove forests. The Rufiji delta covering an area of about 1200 km 2, with its associated 7 distributary channels and other interwoven smaller channels and creeks is home to the largest estuarine mangrove forest in East Africa, with an estimated surface area of 53,200 ha. The Rufiji delta mangrove forest constitutes about 46% of the total mangrove forest cover in Tanzania (Semesi, 1991; Kajia, 2000;. IUCN, 2003). Anthropogenic activities related to demand for water for irrigation and hydropower developments (Figure 9) are considered to have significantly reduced the fresh water discharges of the rivers on the TIO drainage system at list since the last five decades (IUCN, 2003; Shaghude, 2006; Duvail and Hammerlynk, 2007). Anthropogenic activities associated with livestock developments and landuse changes on the upper catchments of the rivers on the TIO drainage system have also contributed to the degradation of the river basins with corresponding reduction in the fresh water discharges of the rivers (Sosovele, 2007). In some of the rivers such as the Pangani, Wami and Ruvu, the situation is considered to be critical with multipliable socio-economic conflicts and potential ecological and environmental impacts at the coast (IUCN, 2003; Shaghude, 2006) In the Rufiji River Basin for instance (Fig. 9), the total annual discharge is estimated at 28, 382 Mm 3 (million cubic metres), which are contributed by the three tributaries on the Upper Rufiji, namely the Kilombero (17, 597 Mm3), the Great Ruaha (4,257 Mm 3 ), the Luwegu (5,109Mm 3 ) and the flows from the Lower Rufiji (1,419 Mm 3 ). Out this total flow, the irrigation developments on the Great Ruaha River consumes about 1,490 Mm 3, while the planned development on the Lower Rufiji is anticipated to consume about 2022 Mm 3 and the evaporative losses from the Mtera dam are estimated at 1,277 Mm 3, making a total reduced flow of about 4,769 Mm 3, equivalent to 153 m/s (Shaghude, 2008) which is also approximately 17% of the Rufiji Basin annual discharges The reduced flow may have profound effects on the dry season fresh water discharges to the sea by\the Rufiji, which is estimated at 300 m 3 /s (Shaghude, 2008). In the Pangani River Basin, the fresh water contribution from mount Kilimanjaro and other sources had been estimated at 500 Mm 3 and 400 Mm 3, respectively (Fig. 9). As with the Rufiji River Basin the reduced flow due to irrigation developments and evaporative losses in dams had been estimated at 400 Mm 3 and 400 Mm 3, respectively. The reduced flow on the Pangani due to the existing irrigation project and the water impoundment in the Nyumba ya Mungu dam would therefore amount to at least 800 Mm 3 per year, which is a very significant proportion (about 89%) of the total available water on the Pangani River Basin. i) Issues Anthropogenic activities have significantly affected fresh water discharges in the TIO drainage system at least during the last five decades (IUCN, 2003; Shaghude, 2006; Duvail and Hammerlynck, 2007). Landuse changes within the upper catchments of the rivers have contributed to the degradation of the river basins with corresponding reduction in the freshwater discharges (Shaghude, 2008). In some of the rivers such as the Pangani, Wami and Ruvu, the situation is considered to be critical with multiple socioeconomic conflicts and potential ecological and environmental impacts at the coast (Mwandosya et al., 1998; IUCN, 2003; Shaghude, 2006; Yanda and Munishi, 2007). The changes in rainfall pattern due to global climate change are also altering the river flow regime in most of the TIO drainage system and parallel impacts at the coast are envisaged (Yanda and Munishi 2007). Coastal environmental impacts due to increasing water abstraction (for irrigation) and hydropower developments as well as the increasing degradation of the catchments due to landuse changes and livestock keeping. There is a general lack of information on the patterns of climate change and their impacts on the hydrology of the Tanzanian river systems draining into the coast. ii) Gaps There is a need for updated data on current river discharges. In this regard, there is a need to further build the capacity for comprehensive monitoring of river discharges. There is also a need to identify appropriate climate change adaptation and mitigation measures in all major river basins of Tanzania. 13

25 2. Biophysical Environment (a) 4,257 Mm 3 17,597 Mm 3 5,109 Mm 3 1,419 Mm 3 Usangu wetlands Kibasila swamps 1,400 Mm 3 1,277 Mm 3 Rufiji R 28,382 Mm Mm 3 DAM IRRIGATED AGRICULTURAL LAND LOWER RUFIJI RUAHA KILOMBERO LUWEGU (b) contribution From Other Mts contribution From Mt Kilimajaro 400 Mm Mm Mm Mm 3 DAM IRRIGATED AGRICULTURAL LAND Fig. 9. Figure 8. Rufiji (a) and Pangani River Basins (b) water budgets. The bold arrows in the figures indicates the estimated annual input of fresh water to the systems, while the dotted arrows indicates the water losses due to irrigation and evaporation. Source: Shaghude (2008). 14

26 2. Biophysical Environment Physical Oceanography Water circulation within Tanzania s coastal waters is controlled by a number of factors, including the Northeast and Southeast monsoons, the East African Coastal Current, the South Equatorial Current and the tidal regime. Currents The East African Coastal Current (EACC), which flows northwards throughout the year, is the dominant prevailing ocean current along the coast of Tanzania (Newell, 1959). The EACC principally originates from the Southern Equatorial Current (SEC) which flows from east to west throughout the year at around latitude 12 o S (Swallow et al,. 1991). The EACC is strongest during the period April to October with current velocities ranging from 1.5 to 2 m/s when it is accelerated by the SE monsoon winds. During the period between November and March, the current is weaker with low velocities of the order 0.5 m/s as it is impeded by the northeast (NE) monsoon winds. Tanzania coastal water is characterised by nutrient-poor water resulting in low productivity (El-Sayed, 1989). The coastal dynamics however, are to some extent influenced by the presence of islands (Zanzibar, Pemba, Mafia and numerous smaller islands), orientation of the coast and an almost continuous band of reefs that fringe the coast and islands. Studies carried out on current velocities in inshore water of Tanzania show that there are significant differences from one location to the other. For instance, in the inshore waters off Kunduchi in Dar es Salaam, the current speed recorded during the NE monsoon, averaged over one tidal cycle, is about 0.25 m/s with a maximum of 0.5 m/s. There is however, no remarkable change in both speed and direction during the SE monsoon. In the Kunduchi-Manyema Creek, velocities of up to 3.5 m/s have been recorded during ebb tide (Dubi, 2006). Within the Zanzibar Channel when the EACC is strongest ( June-October), some flow of the EACC is diverted through the southern entrances of the Zanzibar and Pemba channels (Garcia-Reyes et al., 2009). During the NE monsoon, some of the EACC drives a southward flow through the northern entrance of the Zanzibar Channel. The shores of the southern border of Tanzania and Mozambique at Mtwara are also of strategic importance because this is where the South Equatorial Current (SEC) meets the coastline of Africa and divides. The SEC waters carry eggs and larvae of numerous marine animals and plants. This area is therefore very important for the settlement and subsequent dispersal of marine organisms, both north and south along the coast of East Africa (Obura, 2004) Studies have also shown that in the Rufiji delta freshwater is trapped in the nearshore zone due to the orientation of the delta, the prevailing wind regime (always onshore) and current conditions (Iversen et al., 1984; Francis, 1992). The EACC inhibits the flow of nearshore waters offshore, resulting in greater nearshore current flows (Gupta and Desa, 2001). i) Issues Cyclonic eddies such as those which have been observed at the small island of Latham may be hazardous to fishers and navigators. ii) Gaps Lack of sufficient knowledge of coastal currents and their seasonality. So far only short-term observations covering small areas of interest have been made. Lack of sufficient knowledge of the effect of the EACC on the coastal dynamics. Insufficient knowledge of areas with cyclonic eddies and upwellings. Current patterns in the strategic areas for egg and larval dispersal (such as those in Mtwara and south Mafia) are not clearly understood, there is speculation only. Lack of an inventory of historical surveys and expeditions 15

27 2. Biophysical Environment Tidal regime and waves Tidal ranges Tides along the Tanzanian coast and islands are predominantly semi-diurnal, with a Form Factor of 0.16 (Pugh 1984). The mean spring tidal ranges vary from 3.0 m at Kunduchi in Dar es Salaam (Lwiza and Bigendako, 1988) to a maximum of 3.6 m at Zanzibar harbour (Odido and Francis, 1999; Cederlöf et al., 1995; Mahongo and Francis, 2010). At Dar es Salaam harbour, the mean spring tidal range is about 3.2 m (Lwiza and Bigendako, The maximum tidal range in most places in Tanzania is about 4 m (Hartnol 1974). The times of high and low tides are also approximately the same all along the coast (Ngusaru 2002). Throughout the coast of Tanzania, the mean neap tidal ranges vary from about 0.9 m at Chwaka bay in Zanzibar (Cederlöf et al. 1995) to about 1.2 at Zanzibar harbour (Odido and Francis 1999). The age of the semi-diurnal tide (time interval between the times of new and full moon and a measure of delay period of the spring tide) vary between one and two days. The age has a lag of about 26 hours at Zanzibar harbour (Odido and Francis, 1999), and about 32 hours at Dar es Salaam harbour (Lwiza and Bigendako, 1988). Wave patterns There are a few studies that document wave characteristics of coastal Tanzania, and these have mainly been undertaken on a short-time basis in a few areas of interest. Average wave heights of about 0.9 m have been observed during the North East monsoons, which increase to about 1.2 to 1.5 m during the South East monsoon (Lwiza, 1994; Nyandwi, 1999). During the North East monsoon, wind-generated waves approach the coast from the northerly sector. During the South East monsoon, waves approach the shore from the south-east direction with periods of 8-10 seconds (Nyandwi, 1999). Highest waves are experienced at the peak of the South East monsoon during the period between July and September. In August the significant wave heights are about 0.4 m and wave periods are about 6-10 seconds (Nyandwi, 1999). Generally, fringing reefs protect the coastal areas and islands from most storm waves and swells (Brampton, 1996) and play an important role in refracting and diffusing the waves (Lwiza, 1994). Occasionally however, strong wind waves cross the barrier reefs to reach the shores, especially when spring tides coincide with storms and onshore winds. In addition to causing flooding in low lying areas, strong waves are also responsible for coastal erosion. Makota et al. (2004) for instance, observed considerable changes of the Kunduchi shoreline off Dar es Salaam between 1981 and 2002, whereby between 2.04 ha and 2.60 ha of the beach was eroded by wave action. Recently, Almström and Larsson (2008) concluded wave generated longshore transport is the governing process for moving sediments along the Kunduchi beach area. Lwiza (1994) also recognised the influence of waves on coastal erosion in Tanzania. Tanzania is fortunate in not having experienced a major tsunami event. However, in December 2004, the Indian Ocean Tsunami caused by an undersea earthquake in Indonesia resulted in larger-than-normal waves reaching Zanzibar (Merrifield et al., 2005). i) Issues Coastal erosion which is causing infrastructural damage, loss of valuable land and other impacts with major economic implications. Extreme waves and storm surges that accelerate coastal erosion processes. ii) Gaps The coverage of sea level monitoring is low and tide gauges are yet to be installed in strategic locations along the coast of Tanzania. Lack of capacity for study of waves, sea level analysis and prediction. Lack of sufficient knowledge on the effects of local and regional factors on short-term changes of sea level Lack of capacity in satellite altimetry. Lack of a warning system for storm surges and tsunamis. 16

28 2. Biophysical Environment Sea level change Along the coast of Tanzania, sea level variability is monitored using tide gauges installed in two stations in Zanzibar and Mtwara. The Zanzibar station is considered to be one of the most important Indian Ocean tide gauge stations for monitoring long term changes in sea level in the Western Indian Ocean (Church and White, 2006). The two stations transmit sea level data to the Indian Ocean Tsunami Warning System (IOTWS) on a real time basis through the Global Telecommunications System (GTS). Historical sea level data exist for stations located in Dar es Salaam, Mtwara and Tanga. However, data from these stations cover relatively short periods. A recent study of trends in mean sea levels in Tanzania indicates falling sea level in Tanga (between 1962 and 1966), Dar es Salaam (between 1986 and 1990) and Zanzibar (between 1984 and 2004). However, sea level is rising in Mtwara (between 1959 and 1962) (Mahongo, 2009). Data from Zanzibar indicate that sea level has been declining at a rate of 3.6 mm/year for the period between 1985 and Mahongo and Francis (2010) have also given an in-depth analysis of the seasonal variations of sea level at the island of Zanzibar during the period , revealing three major cycles of sea level i.e. semi-annual, annual and four-year oscillations. Few studies on the past sea levels along the coast of Tanzania have been undertaken. In Tanzania, Muzuka et al. (2003) made a preliminary investigation on the Pleistocene/Holocene sea level changes. In this study, it was found that the oldest Palaeo-shoreline is approximately 5 m above the present sea level. This extends landward to more than 1 km. On the islands of Zanzibar, specific localities where Pleistocene/Holocene sea level changes occurred have been preserved in the form of marine terraces and/or beach ridges. These are found in Chwaka, Uroa, Jambiani, Paje and Nungwi in Unguja Island and, Vumawimbi and Kiuyu in Pemba Island (Muzuka et al. 2000; Alexander, 1969 & 1985). Projections of future mean sea level trends in Tanzania are currently not feasible due to insufficient data occasioned by limited duration of monitoring. The longest sea level record is only 25 years at Zanzibar. However, model simulation of long-term sea level trends ( ) using a combination of tide gauge records and satellite altimetry, show a general rising trend in Tanzania ranging from 0.4 to 2.0 mm/yr (Bindoff et al., 2007). The global average within this period is about 0.4 to 3.6 mm/yr (Bindoff et al. 2007). i) Issues Increased coastal erosion along the coast causing major economic losses due to loss of land and infrastructural damage. Inundation and displacement of wetlands and lowlands due to flooding. Saltwater intrusion into estuaries and groundwater aquifers. Changes in sedimentation patterns. Increased turbidity of coastal waters reducing productivity. ii) Gaps Lack of sufficient knowledge of factors affecting long term change in mean sea level Lack of long term sea level records. Lack of capacity in the analysis of satellite altimetry data. Ocean temperature Sea Surface Temperature (SST) Typically, the average Sea Surface Temperature (SST) in Tanzanian offshore waters is around 27 o C and the typical range is from 22 to 30 C (Newell, 1957; Iversen et al. 1984; Francis et al., 2001). The SSTs are generally higher during the North East monsoon as compared to the South East monsoon. The SSTs are also highest in early March and lowest in either August or September (Harvey, 1977). However, higher SSTs of up to 32.5 o C occur in shallow coastal areas (Lugomela, 2006). During the North East monsoon, there is a decrease in water temperature with depth while during the South East monsoon the waters are isothermal from the surface to the thermocline. According to Hartnoll (1974) 17

29 2. Biophysical Environment and Harvey (1977), the thermocline in the Tanzanian offshore waters lies at a depth of between 25 and 100 m. The temperature of the mixed layer varies quite appreciably from one place to another, mainly due to seasonal variations. There are also diurnal variations particularly in offshore waters which are controlled by variability in the heating of water by the solar radiation during the day and cooling during the night. In the near-shore waters, the seawater temperatures are mainly semidiurnal due to dominant effect of the semi-diurnal tides (Francis et al., 2001). In Zanzibar, SSTs have been recorded using temperature loggers tied on coral branches at 3 m depth on Bawe and Chumbe coral reefs (Muhando 2001). Recording undertaken since 1997 showed a yearly seasonal pattern with lowest temperatures ranging C occurring in July August, with an annual peaks (29.2 C C) occurring in the period between March and April. Generally, mean SSTs are always higher during the North East monsoon (about 28 C) than during the South East monsoon (about 26 C). Intrusion of a cold seawater mass in January February period is attributed to the northward flow component of the EACC (Garcia-Reyes et al., 2009). i) Issues Coral bleaching due to increased Sea Surface Temperatures (SSTs) Fish kills due to harmful algal blooms. Loss of colour and hence value of seaweeds. ii) Gaps Lack of sufficient knowledge of seasonal and spatial variation of SSTs in most areas. Lack of vertical temperature profiles- only short-term measurements on SSTs which are site specific. Salinity patterns The surface water salinity of the Tanzanian coastal waters ranges between 34 and 36 PSU. In estuaries and coastal bays, salinities are usually relatively low due to the influence of freshwater discharge from the river systems. The salinities in offshore waters are highest in November during dry season, and are lowest in May during rainy season following the peak river freshwater outflow (Iversen et al. 1984). Bryceson (1982) observed that the salinity starts to decrease before the onset of the rains and attributed this to the advection of lower salinity water from the South. The salinity of the surface water at Kunduchi in Dar es Salaam reaches a maximum of about 35.3 PSU in November and falls to a minimum of 34.6 PSU in May (Hartnoll, 1974). In the Mafia Channel, the salinity ranges between 34.7 and PSU while in the Rufiji delta, salinity range PSU inside the estuary and PSU at the mouth of the delta (Talbot, 1964; Tafe, 1990). On the East coast of Zanzibar at Chwaka Bay, salinity ranges from PSU on the inner zone of the bay and ranges from PSU at the entrance (Lugendo et al., 2005, Wolanski, 1989). During the dry season, the salinity in the inner mangrove areas of Chwaka Bay can reach 38 PSU. Water masses of the Tanzanian coast There are four water masses in the Tanzanian offshore waters, characterized by typical salinity and oxygen levels. These occur at various depths. They include: (i) Tropical Surface Water characterised by high salinity and high oxygen, (ii) Arabian Sea Water at depth of about 1000m characterized by high salinity and low oxygen, (iii) Antarctic Intermediate Water characterized by low salinity and high oxygen, and (iv) North Indian Deep Water characterized by high salinity and low oxygen (Hartnoll, 1974). The Tropical Surface Water originates from the South Equatorial Current (SEC). Ocean-atmosphere interaction Few studies have been undertaken on ocean-atmosphere interactions in Tanzania. A study on heat fluxes at Chwaka bay on the eastern coast of Zanzibar in 1996 established that the major heat fluxes within the bay were due to incoming solar radiation and loss due to evaporation and long-wave back radiation (Mahongo 1998, 1999, 2000). The sensible heat and net long-wave radiation fluxes played minor roles in the heat budget of the bay. The observed and computed values of the fluxes of absorbed solar radiation, evaporation, net long-wave 18

30 2. Biophysical Environment radiation, sensible heat and reflection at the bay bottom were respectively +275, -156, -38, -18 and -2 W m -2. The heat budget was mainly balanced by heat advection from the bay to the open ocean, with a small portion being due to water-sediment heat conduction (Mahongo 1998, 1999, 2000). The Indian Ocean Dipole and El-Nino Southern Oscillation (ENSO) phenomenon have some significant influences on the climate of coastal region of Tanzania. However, there are few local studies that have focussed on these two phenomenons. Kijazi and Reason (2005) has established that El Nino is associated with above average rainfall while La Nina is associated with below average rainfall over the northern region of the Tanzanian coast during the North-East Monsoon season, and to lesser extent during the South-East Monsoon season. Chemical and Biological Oceanography Nutrients Increased economic activities and expanding populations in coastal towns of Tanzania have resulted in production of large amount of waste including sewage and industrial effluent. Unfortunately, raw sewage and industrial effluents produced in all coastal towns are directly released into estuaries and other coastal habitats. This is particularly evident in Dar es Salaam, Zanzibar, Tanga, Kilwa and Mtwara. Away from coastal towns, pollution of coastal waters is caused by fertilizer residue contained in run-off from agricultural areas. There is evidence of nutrient enrichment. For instance, high nutrient loads have been detected in waters fronting major towns in Tanzania. Ammonium levels of up to 28.6 μg-at Nl -1, nitrate levels up to 7.8 μg-at Nl -1 and phosphate levels of 4.0 μg-at Nl occur -1 in Zanzibar (Anderson, 1994). Furthermore, high amounts of faecal coliform and total coliform bacteria of up to several thousands per ml of seawater, occur in the waters off Stone Town, Zanzibar (Mohammed, 2001). Likewise, high nutrient loadings have been recorded in water fronting Tanga Township. Effluents from a fertilizer factory, municipal sewage and sisal decortications plants have enriched coastal waters causing proliferation of macroalgae in Tanga coastal waters (Munisi, 1999; Shilungushella, 1993). In Dar es Salaam, the inshore waters are characterized by the presence of high levels of nutrients (Lyimo (2009). Nitrate levels of up to 54 μmoll -1, phosphates of up to 45 μmoll -1 and nitrites of up to 20 μmoll -1 have been recorded. Several thousand counts of microbials ranging between 1,700 and 240,000 for total coliform, 200 to 92,000 for faecal coliform and 11 to 4,900 for enterococci have also been observed in Dar es Salaam inshore waters. The levels of faecal indicator bacteria and nutrients are usually higher during the rainy seasons due to surface runoff from Dar es Salaam city (Bryceson, 1983). The coastal areas of Dar es Salaam experience heavy loads of pollutants through Msimbazi Creek which receives large quantities of domestic and industrial wastes from the city of Dar es Salaam. The river and creek receive pollutants such as dyes, paint wastes and strong alkalis, oil and tars, as well as organic wastes from breweries and meat plants (Bryceson, 1982). In Dar es Salaam, raw sewage generated by 15% of the city residents who are connected to the sewer system is discharged directly into the sea, untreated. The situation became worse in the 1990s due to damage of the sewer pipe leading to the discharge of untreated sewage on sandy-mud flats near the harbour (Bryceson et al., 1990). About 79% of the population in Dar es Salaam use onsite sanitation facilities particularly pit latrines (Mashauri and Mayo 1989; Mgana and Mahongo, 1997; Dar es Salaam City Council, 2004). Leachate and overflow from pit-latrines have led to contamination of most surface and groundwater resources including inshore waters. Other sources of coastal pollution in Dar es Salaam are industrial wastes from Keko, Chang ombe, Kurasini, Mtoni and Temeke which discharge heavy metals, pesticides, paint, nutrients, organic and other pollutants near the harbour (Bryceson, 1983; Machiwa, 2000; Mwevura et al., 2000). Other coastal areas of Tanzania outside the major cities and townships are free from domestic wastes but occasionally suffer from input of agricultural wastes, including pesticide and fertilizer residues. Most of the major rivers in the country drain rich agricultural lands where the application of fertilizers and pesticides to boost crop production is common. 19

31 2. Biophysical Environment Persistent organic pollutants High levels of PCBs and organochlorine pesticide residues have been detected in Dar es Salaam harbour (Machiwa, 1992; Mwevura et al. 2002). Chlorinated compounds due to pesticide pollution have been reported in Chwaka bay, Zanzibar (Mmochi, 2005). Heavy metals such as lead (Pb), zinc (Zn), cadmium (Cd), chromium (Cr), mercury (Hg) and copper (Cu) have been reported in waters within Dar es Salaam harbour and nearby coastal areas (Machiwa, 1992; Kondoro 1997; Muzuka, 1997). Concentrations of these metals exceeded maximum values recommended by the World Health Organization (WHO). Similarly, high concentrations of Cr, Pb, Cu, Hg and other heavy metals have been reported in Mzinga creek mangrove sediments in Dar es Salaam (Mtanga and Machiwa, 2007). These metals were found to have accumulated in tissues of Polychaete worms (Mtanga and Machiwa, 2007). Several studies have also been conducted on the impacts of heavy metal on flora and fauna dwelling in polluted habitats in Dar es Salaam coastal areas (Mwandya, 1996; Wekwe et al. 1989). The environmental impacts of Pb, Hg and Cd on calcification rates of the reef building calcareous algae Amphipora tribulis have been investigated in Dar es Salaam (Kangwe, 1999). Primary production In Tanzania, high plankton biomass and productivity occur during the NE monsoon and is relatively lower during the SE monsoon period. The biomass is usually highest at the surface water column especially during calm weather periods (McClanahan, 1988; Lugomela et al., 2002). The water column primary productivity ranges from 204 to 4142 mg C m 2 day 1. Bacterial production varies from 10 to 72 mg C m 2 day 1, comprising 5% of the total bacterial standing stock (Lugomela et al, 2001). Biofilm carbon fixation rate is estimated to be 0.05, 0.3 and 0.5 kg C m 2 y 1 for thin (0.5 mm), medium (1 mm) and thick (2 mm) biofilms, respectively with an overall primary production rate of 0.14 kg C m 2 y 1 at depths of about 5 m (Lugomela et al. 2005). The nitrogen fixation rate in intertidal sediments along the coast of Tanzania is estimated to be 38 mmoln m -2 y -1. Higher rates of nitrogen fixation occur during the night time as compared to daytime suggesting sediments composed of non-heterocystous diazotrophic organisms (Lyimo and Lugomela 2006). The rates of nitrogen fixation by Trichodesmium species in the surface waters were estimated by to be 42.7 mmol N m -3 y -1 (Lugomela et al., 2002) In Zanzibar, studies on nitrogenase activity found that nitrogen fixation varies from 6.0 to nmol C 2 H 4 cm - 2 h -1 on mangrove pneumatophores and from 1.3 to 16.8 nmol C 2 H 4 cm -2 h -1 in adjacent sediments (Lugomela and Bergman, 2002). In sandy and muddy areas within a mangrove ecosystem near Zanzibar town, the rates of nitrogen fixation are of the order of 1.64 and 1.34 nmol N m -2 h -1, respectively, (Kyaruzi et al., 2003). Studies on the impact of mangrove deforestation on nutrients, phytoplankton community structure and biomass in Tanzania have established that there are no significant differences in both water-column and sediment phytoplankton biomass between deforested and conserved sites (Kyewalyanga, 2005). Sediment chlorophyll-a was however significantly higher at the conserved site (average of 2.38 ± 1.36 mg m -3 ) than at the deforested one (1.28 ± 0.91 mg m -3 ), while water-column chlorophyll-a was higher at the deforested than at the conserved site, with averages of 1.52 ± 1.26 and 0.71 ± 0.62 mg m -3, respectively. Organic matter content was much higher at the deforested site (25.98 ± 1.51%) compared to the conserved mangrove site (19.52 ± 0.99%) (Kyewalyanga 2005). Studies on the cyanobacteria diversity and nitrogenase activity in Paje lagoon, Zanzibar have revealed rich cyanobacterial genetic and morphological diversity and substantial nitrogenase activity especially during the night with the maximum activity reaching 120 nmol C 2 H 4 cm 2 h -1 ) (Bauer et al., 2008). Several potentially harmful microalgae have been found in Tanzanian coastal waters. They are distributed among three major microalgal groups, namely cyanobacteria, mostly dominated by Trichodesmium spp, the dinoflagellates, dominated by both Prorocentrum spp. and Gambierdiscus toxicus and the diatoms, mostly Pseudonitzschia spp. (Hansen et al., 2001; Lugomela, 2006 & 2007). Relative abundance and spatio-temporal variability of these organisms has not been well assessed. It is also not known if these organisms are associated with severe poisoning associated with the consumption of shellfish and meat from dead turtles that has happened at several places along the coastal line of Tanzania (The independent 1996, promed-mail 1996). 20

32 2. Biophysical Environment Secondary production In the inshore waters of Dar es Salaam, the main taxa of zooplankton are Calanoida (49. 1%), Larvacea (11. 9%), Corycaeus spp. (6.4%), Cypridina sinuosa (5.6%), Oithona spp. (4.8%), caridean larvae (4.0%), Sagitta spp. (3.8%), Euterpina (2.1%), Lucifer (1.2%), Oncea (1.2%), Hydromedusae (1.0%), Euconchoecia chierchiae (1.0%), Creseis acicula (1.0%), Brachyuran zoeae (0.8%), Ctenophora (0.5%), Mysidacea (0.5%) and other minor species (Okera 1974). All major groups of the zooplankton have an annual cycle of abundance, with relatively high numbers being recorded in the period between February and August during the SE Monsoon. During the NE monsoon, the abundance is relatively low. Relatively richer, more diverse fauna exist at the river mouths and estuaries compared to the upper reaches as demonstrated in the Rufiji Delta (Tafe, 1990). The zooplankton in river mouths and estuaries are more abundant at certain times of the day. However, differences in faunal composition are found between different areas (Tafe, 1990). Estimates of total zooplankton in the Zanzibar coastal area was carried out by Wickstead in There is a need for updating of information on zooplankton in view of the fact that previous studies are now outdated and many changes have taken place. A few studies on trophic relationships have also been conducted in Tanzania coastal-marine waters. Lugomela et al. (2001) has shown that 77% of the total primary production is channeled through the heterotrophic flagellates, ciliates and heterotrophic dinoflagellates to higher trophic levels. Thus, 28% of estimated carbon demand for mesozooplankton could potentially be met by ciliates and heterotrophic dinoflagellates (Lugomela et al. 2001). Another interesting investigation was done on the feeding behaviour of chaetognath species between the monsoons periods conducted in Zanzibar in The diet, feeding behaviour, feeding rates and estimates of predation impact on standing stock of copepods as well as the impact of cannibalism were presented in this study (Oresland 2000). Coastal Zone and Continental Shelf Description and extent of coastal and marine habitats The coastal zone of Tanzania stretches from latitude 4º49 S at the border with Kenya to the border with Mozambique at latitude 10º28 S. About two thirds of the coastline has fringing reefs, often close to the shoreline, broken by river outlets such as the Rufiji, Pangani, Ruvuma, Wami and Ruvu (Dubi 2001). Features of interest within the coastal zone include the coastline, continental shelf, corals, mangroves, and seagrass beds. The length of the coastline of Tanzania is 3,461 km (United States Mapping Agency, 2003). The width of the continental shelf is 5.8 km except in the Zanzibar and Mafia channels where it reaches a width of about 62km. The total area of the continental shelf is estimated to be 17,900 km 2. The most important coastal ecosystems include coral reefs, mangroves and seagrass beds. Coral reefs Coral reefs cover about two thirds of Tanzania s continental shelf. Fringing reefs forming margins along the edge of the mainland or islands and patch reefs dominate the coastal waters of Tanzania (TCMP, 2001a). Due to the restricted drainage and un-indented coastline, well developed coral reefs have only evolved along major sections of the continental shelf. These cover a surface area of about 3,500 Km 2 - the largest area covered by coral reefs in the entire Eastern Africa. Due to narrowness of the continental shelf, the coral reefs are generally situated near the shoreline within a distance of between 1 and 5 km. The coral reefs in Tanzania are under different types of threats. In some Marine Protected Areas (MPAs) and managed areas (e.g. Muheza, Tanga and Pangani Districts), most of the destructive fishing practices has been stopped. However, dynamite fishing, coral bleaching, seine netting, over-fishing, shell collection, wave action, boat anchoring, coral mining, crown-of-thorns starfish (COTS) and pollution are still the main threats to the existence of the coral reefs (Francis et al., 2001; Horril et al., 2001; Ngusaru et al., 2001; Whitney et al., 2003). The coral reefs in Tanzania have also been impacted by rising seawater temperatures. In the period between March and September 1998, a significant coral bleaching event occurred leading to 15 to 100% damage to hard corals. Bleaching was worse in shallow waters than in deeper waters (TCMP, 1999; Muhando, 2003). The coral reefs of Zanzibar and those found in MPAs are generally in good condition since they have escaped 21

33 2. Biophysical Environment from serious mortality driven by bleaching events (Wells et al., 2004). This is also the case in well managed sites such as Chumbe where the diversity of fish populations is higher as compared to over-fished coral reefs found off Dar es Salaam and Tanga (McClanahan et al., 1999). Reefs around Pemba are extensive, luxuriant and diverse but only few studies have been carried out on them (Wells et al., 2004). Mangroves A total of 8 species of mangrove, namely Avicennia marina, Bruguiera gymnorrhiza, Ceriops tagal, Heritiera littoralis, Lumnitzera racemosa, Rhizophora mucronata, Sonneratia alba and Xylocarpus granatum are found in mainland Tanzania. In addition, Xylocarpus mulluccensis occurs in Zanzibar (Ngusaru et al, 2001). The mangrove ecosystem in Tanzania is under threat due to high demand for mangrove products such as firewood, charcoal, building, boat making, in addition to commercial cutting and over harvesting, coral burning, lime production, salt making, clear-cutting for building sites, solar salt pans, commercial projects and clearance for agriculture (Shunula and Whittick, 1996; Francis et al., 2001; Wagner, 2003). There has also been a decline in mangroves forests due to natural factors. For instance, in the Rufiji delta, the mangrove forests have declined slightly from 49,799 ha in 1990 to 49,032 ha in 2000 due to flooding of Rufiji River (Wang et al. 2003). The other main threats to the mangroves include coastal erosion and clear cutting for construction (Francis et al., 2001), clear felling for paddy farming and illegal harvesting (Sallema, 2003). The use of DDT and other pesticides on rice farms and the construction of dams and major irrigation schemes upriver are also possing a threat to the mangroves (Semesi and Mzava, 1991). In Zanzibar, mangrove threats include rice cultivation and debarking of Rhizophora sp. for tannin production (Wells et al. 2004). This is particularly noticeable in Pemba (Wete District). Mangroves in Zanzibar are also threatened by cutting for fuel, the coral mining industry, firewood, building poles and boat making. Although Micheweni has most important stands with large mangrove trees in Zanzibar, it is threatened by selective cutting and high demand for lime production. In Unguja Island, most mangrove trees are small and few reach 10 m in height as the large ones have been cut for timber and firewood (Shunula and Whittick, 1996). There has been intensive cutting of mangroves in Chwaka Bay. Mangroves are also degraded near Maruhubi (2 km north of Zanzibar town) as a result of high demand for mangrove products by the local community (Kulindwa et al., 2001). Seagrass beds In Tanzania seagrass beds are widespread and are found in all bays in most inshore areas and on the west side of most islands. The most extensive seagrass beds are found in Tanga coast, deltas of Ruvu, Wami and Rufiji rivers, Mafia and Songo songo archipelago and around Kilwa. There are 12 species of seagrass off the coast of Tanzania. The area covered by seagrass beds and the relative species densities in Tanzania are however not known (Whitney et al. 2003). Seagrass beds in Tanzania are threatened by natural and human activities that include illegal fishing practices such as beach seining and shallow water trawling (Francis et al., 2001; Muir et al., 2003; Whitney et al., 2003), anchoring of fishing and tourist boats, excessive sedimentation increasing turbidity and reducing light penetration and shoreline dynamics involving sand deposition and removal (Whitney et al. 2003, Wells et al., 2004). Natural grazers such as sea urchins and dugongs have also in some places reduced the cover of seagrass beds (Francis et al. 2001, Whitney et al., 2003). Issues The main issues in as far the critical ecosystems are concerned include increasing degradation of the ecosystems due to various anthropogenic activities including destructive fishing methods and overexploitation. The rapid increase in coastal population is putting high pressure on finite coastal natural resources. Degradation of critical coastal ecosystems has the potential to reduce the ecosystem goods and services offered by these mangroves, coral reefs and seagrass beds. This has the potential to affect the socioeconomic livelihoods of the local communities in Tanzania. 22

34 2. Biophysical Environment ii) Gaps Lack of information on the impacts of sedimentation of coral reefs, seagrass beds and mangrove forests. Lack of information on the key features of some coral reefs. Lack of comprehensive descriptions and identification keys for Tanzanian coral species. Lack of regular systematic monitoring for coral reefs. Lack of detailed information on cover and species densities of seagrass beds and extent to which threats pose a problem. Lack of maps showing distribution of seagrass beds and coral reefs. Lack of current nationwide information on mangroves stock, condition and diversity. Lack of current information on mangrove changes from year 2000 to date. Productivity of the Coastal zone The coastal and marine environments of Tanzania are characterized by high marine biodiversity and rich marine and coastal resources which amongst others, include major estuaries, mangrove forests, coral reefs, sandy beaches, cliffs, seagrass beds and muddy tidal flats (Francis and Bryceson, 2001). Rivers such as Pangani, Wami, Ruvu, Rufiji, Matandu, Mbemkuru, Lukuledi and Ruvuma all flow to the Indian Ocean and to a certain extent influence the coastal environment through creation of productive brackish water environments in estuaries, maintenance of deltas, tidal flats and shorelines and nourishment of mangroves and seagrass beds (Francis and Bryceson, 2001). These coastal ecosystems subsequently interact with each other and together sustain a tremendous diversity of marine life, which supports the livelihood of coastal communities. A wide range of important and valued species are found along the coast, including an estimated 150 species of corals in 13 families; 8,000 species of invertebrates; 1,000 species of fish; 5 species of marine turtles, and many seabirds (Francis and Bryceson, 2001). Coral reefs Coral reefs support one of the most productive and diverse marine ecosystems in Tanzania waters and, with their associated habitats support a variety of marine species. Over 500 species of commercially important fish and other invertebrates are commonly found in coral reefs. It is estimated that 95% of artisanal fishing, which employs over 50,000 full time fishermen, is carried out on coral reefs. Coral reefs also support over 70% of the artisanal fish production in Tanzania (Saada, 2005). It is estimated that a sustainable yield of 15 tonnes of fish can be obtained per km 2 in depth of less than 30 m in some coral reefs (Munro and Williams, 1985). Generally, there is good coral reef growth and a high coral diversity in many areas in coastal Tanzania. Hamilton and Brakel (1984) recorded 140 coral species in Tanzania. Mafia Island has extensive reefs especially in the south, many in good condition. Medium diversity is found on the reefs of Mnazi Bay (Mtwara), Kunduchi (Dar es Salaam) and Tanga region. Overall reef health is probably good in most parts especially in less accessible and deeper areas i.e. the Mafia, Songo Songo and Kilwa (Saada 2005). The most degraded coral reefs are those found in shallow waters (1-10 m), especially near urban centres of Tanga, Dar es Salaam and Mtwara (Mohammed et al. 2002). Over the past few decades, a number of factors have contributed to the degradation of coral reefs. The closeness of the reefs to land make them particularly prone to human impact, either from exploitation or from indirect terrestrial influence such as sedimentation and pollution. Many of the reefs were severely affected by the coral bleaching event of that reduced the average live coral cover from 52% before bleaching to about 27% after the event (Wells et al., 2004). Follow-up assessments and monitoring indicated that although the impacts were not uniform, generally recovery has been very slow (Mohammed et al., 2002). Corals are also harvested by the local population, to exploit their rich biological and mineral value for jewellery, ornaments and building purposes. Mangroves Mangrove ecosystems include much more than just the trees and encompass terrestrial, fresh water, marine and estuarine systems. According to Francis et al., (2001), there are 8 common species of mangroves in Tanzania mainland either in pure stands or in mixtures (Figure 9). The relatively good condition and high species diversity in the mangrove communities provides important ecological and socio-economic services. Apart from shoreline protection, pollution filtration, and nutrient and sediment trapping, the most notable is their function 23

35 2. Biophysical Environment as breeding and nursery grounds for valuable fish and shellfish species and feeding and protection of various mammals and bird species (Francis et al. 2001). Figure 9: Species Composition of Mangroves in Tanzania (Source: Francis et al. 2001) Coastal communities use mangroves to supply local needs for fuelwood, charcoal making, fences, house construction, boat building, fish traps, fish stakes and for medicine. It is estimated that over 150,000 people make their living directly from mangrove resources in Tanzania (Saada 2005). The largest mangrove forest in Tanzania is found in the Rufiji Delta. Commercial fisheries of crabs, prawn and fish are directly dependent on the mangrove ecosystems thus the two main prawn fishing grounds are areas adjacent to the Rufiji Delta and Bagamoyo. Likewise the fishing for crab is an important activity in the Pangani river mangroves. The direct value of the mangrove habitat which includes values for the fuelwood, timber and poles and wood products, the animals and birds and the honey it provides has been estimated to be USD 0.9 million per year (Turpie 2000). Seagrass beds Seagrass beds are highly productive and serve many ecological functions. Seagrasses form dense beds that cover large areas of sandy or muddy coastal bottom. The species found in Tanzania include Cymodocea rotunda, C. serrulata, Cymodocea sp., Enhalus acoroides, Halodule wrightii, H. uninervis, Halophila minor, H. ovalis, H. stipulacea, Syringodium isoetifolium, Thalassodendron ciliatum and Thalassia hemprichii) (Whitney et al., 2003). The most dominant species are T. ciliatum, T. hemprichii and S. isoetifolium (Francis et al., 2001). Usually several seagrass species occur together in mixed stands that forms extensive meadows. Their importance results from their ecological interactions with other ecosystems in the marine environment, especially mangroves and coral reefs, and in their wide range of physical functions (Saada 2005). Sea grasses are associated with nitrogen fixing microorganisms and support complex food webs through dead and living biomass. Thus, among other services, they provide breeding, nursery and feeding areas for a number of invertebrates and vertebrate species including commercially important species of finfish and shellfish (Wells et al., 2004). Moreover, seagrass roots filter and bind sediments and thus prevent sedimentation over coral reefs hence protecting the shoreline from erosion (Saada 2005). Recent studies of dugong distribution and migration along the Tanzania coast show that they are associated with areas of extensive seagrass beds particularly in the Rufiji delta and Mafia-Kilwa area which has a viable dugong population. i) Issues The main issues are over-exploitation of mangroves, unsustainable mangrove harvesting, pollution, sedimentation, clearance of mangrove areas for agriculture, construction of salt pans and coastal development. 24